The present invention disclosed herein relates to an optical communication system, and more particularly, to a feedback amplifier for receiving an input signal regardless of the size of the input signal.
An optical access network evolves into the form of an optical multiple access using a passive optical network (PON). Such a passive optical network system uses an optical signal in a burst mode. An optical signal in the burst mode changes drastically and abruptly when a packet in one channel switches into a packet in another channel. Accordingly, an optical receiver requires a high reception sensitivity in addition to a wide dynamic range. A preamplifier is disposed at the first state where a signal is inputted in the optical receiver and the performance of the preamplifier is determined depending on the performance of a feedback amplifier.
In this way, the feedback amplifier used in the preamplifier detects a burst packet input signal and includes an amplifier circuit for amplification. A feedback circuit is provided in the feedback amplifier to detect the peak value of a burst packet input signal, and control the level of an output voltage of a detected signal. Here, the feedback circuit includes a feedback resistor connected between an input terminal and an output terminal and a feedback transistor connected in parallel to the feedback resistor. Here, the feedback transistor controls a current flowing through the feedback circuit and an output voltage when a control signal is applied to the base.
In this way, the feedback amplifier detects a burst packet input signal with a voltage level. However, if the voltage level of a burst packet input signal is very low, the feedback amplifier may not detect the burst packet input signal.
Moreover, a method of applying a control signal to the base of a feedback transistor includes a method of generating a control signal by configuring an additional gain control signal generating circuit outside a feedback amplifier and a method of self-generating a control signal by positioning a bias circuit in a feedback amplifier. However, since a control signal changes in response to an input signal, if there is a great difference between input signals, the gain of a preamplifier may not be freely adjusted.